Process for treating cellulosic material with formaldehyde in liquid phase and sulfur dioxide

ABSTRACT

The dimensional stability, crease retention, wrinkle resistance and smooth drying characteristics of a cellulose fiber-containing material such as a cotton fabric are improved by impregnating the material with an aqueous formaldehyde phase and curing the formaldehyde-containing material at high temperature in the presence of catalyst-forming sulfur dioxide while governing the amount of water in the system to provide a self-limiting reaction system, water being the limiting factor in the reaction by which an acid curing catalyst is formed from formaldehyde, sulfur dioxide and water. The aqueous formaldehyde phase may be applied to the material as such, or it may be formed in the material by exposing the latter in a humidified state to formaldehyde vapor. Sulfur dioxide may be introduced into the system either in the course of the aqueous impregnation step or in the curing step.

United States Patent [1 1 Swidler et al.

PROCESS FOR TREATING CELLULOSIC MATERIAL WITH FORMALDEHYDE IN LIQUID PHASE AND SULFUR DIOXIDE Inventors: Ronald Swidler, Palo Alto;

Katherine W. Wilson, Newport Beach, both of Calif.

Cotton, Incorporated, New York. NY.

The portion of the term of this patent subsequent to Dec. 19, 1989, has been disclaimed.

Filed: Feb. I4, 1973 Appl. No.1 332,332

Related U.S. Application Data Assignee:

Notice:

U.S. Cl. 8/I16.4, 8/[25 Int. Cl D06m 13/12 Field of Search 8/! [6.4, 125

References Cited UNITED STATES PATENTS 2/!972 Getchell et a]. 8/l 16.4 X

[ *Oct. 15, 1974 3,653,805 4/1972 Gamarra et al 8/l l6.4 3,660,013 5/1972 Payet et al. .r 8/l 16.4 3,663,974 5/!972 Watanabe et al 81116.4

Primary Examiner-Stephen J. Lechert, Jr. Attorney, Agent, or Firm-Burns, Doane, Swecker & Mathis [57] ABSTRACT The dimensional stability, crease retention, wrinkle resistance and smooth drying characteristics of a cellulose fiber-containing material such as a cotton fabric are improved by impregnating the material with an aqueous formaldehyde phase and curing the formaldehyde-containing material at high temperature in the presence of catalyst-forming sulfur dioxide while governing the amount of water in the system to provide a self-limiting reaction system, water being the limiting factor in the reaction by which an acid curing catalyst is formed from formaldehyde, sulfur dioxide and water. The aqueous formaldehyde phase may be applied to the material as such, or it may be formed in the material by exposing the latter in a humidified state to formaldehyde vapor. Sulfur dioxide may be introduced into the system either in the course of the aqueous impregnation step or in the curing step.

11 Claims, N0 Drawings PROCESS FOR TREATING CELLULOSIC MATERIAL WITH FORMALDEHYDE IN LIQUID PHASE AND SULFUR DIOXIDE CROSS-REFERENCE This application is a continuation-impart of Ser. No. 237,056, filed Mar. 22, 1972 and now abandoned,

- which in turn is a continuation-in-part of Ser. No.

BACKGROUND OF THE INVENTION In recent years various methods have been devised for treating cellulosic fiber-containing products, such as cloth made of cotton or cotton blends, in order to impart durable crease retention, wrinkle resistance and smooth drying characteristics thereto. For example, cellulosic materials have been crosslinked with formaldehyde, giving durable crosslinks having good resistance to repeated laundering and also to various acids and alkalis, and chlorine bleaches. These formaldehyde treated cellulosic materials are resistant to discoloration and yellowing, and are less likely to produce a rash or other sensitization on the wearer than cellulosic materials treated with resins or precondensates of the urea-formaldehyde or substituted urea-formaldehyde types which may decompose and release formaldehyde while in usev However, while formaldehyde has made a significant contribution to the cotton finishing art, the results have been far from perfect. For instance, in some cases the formaldehyde crosslinking treatment has tended to lack reproducibility, since control of the formaldehyde crosslinking reaction heretofore has been difficult. When high curing temperatures were used with an acid or potential acid catalyst, overreaction and degradation of the cotton often happened which considerably impaired its strengthv On the other hand, when attempts were made to achieve reproducibility at temperatures of 50C. or less, much longer reaction or finishing times were usually required, rendering the process economically relatively unattractive. This has been particularly true when sulfur dioxide was used as a catalyst in the previously known processes such as that disclosed in U.S. Pat. No. 3,663,974 or the corresponding British Pat. No. 980,980. In other cases, formaldehyde crosslinking has not been able to meet commercial standards with respect to dry wrinkle recovery. For these and similar reasons efforts have been continuing to develop new and better finishing processes for cotton and other cellulose fiber materials.

For the sake of completeness it may also be mentioned that it has been previously suggested in U.S. Pat. No. 2,870,041 that formaldehyde odors in fibrous material which has been treated with a urea-formaldehyde or melamine-formaldehyde type crosslinking resin can be prevented by treating such material with an aqueous solution of sodium meta bisulfite or of some sulfite or bisulfite salt which supplies HSO ions to the system and forms a stable addition product with formaldehyde.

However, in such a system formaldehyde is not used as the creaseproofing agent and the "stabilization" of the formaldehyde in the system does not serve to creaseproof it. On the contrary, a customary dry high temperature cure of the material containing the melamine-fonnaldehyde or other crosslinking resin in the presence of a latent curing catalyst is required, which in turn requires removal of the salt catalyst from the cured fabric by washing. The possiblity of using sulfur dioxide in aqueous solution as the formaldehydebinding agent is also suggested in said U.S. Pat. No. 2,870,041. However, as only an unstable hydroxy methyl sulfonic acid is formed from formaldehyde and sulfur dioxide in the presence of water and this acid reverts to fonnaldehyde and sulfur dioxide on drying, it is evident that this previously suggested use of aqueous sulfur dioxide can not serve as an effective means either for the permanent removal of formaldehyde odors nor for any other significant improvement of the resintreated material.

DESCRIPTION OF THE INVENTION A primary object of the present invention is to provide a practical process for treating cellulose fibercontaining materials with formaldehyde to improve their shape holding properties while avoiding or alleviating the problems mentioned above.

A more specific object has been to develop a process for crosslinking cotton-containing fabrics with the aid of formaldehyde which is deposited in the fabric in aqueous phase, forming the required strong acid catalyst in the process substantially in the amount needed by reaction with sulfur dioxide under controlled and self-limiting conditions, thereby keeping acid injury to the fiber to a minimum while avoiding the need for after-washing.

These and other objects, as well as the scope, nature, and utilization of the invention will become more clearly apparent from the following more detailed description. Unless otherwise indicated, all proportions and percentages of materials or compounds are expressed on a weight basis throughout this specification and appended claims.

In accordance with the present invention, a process is provided for treating a cellulose fiber-containing material to improve its dimensional stability, crease retention, wrinkle resistance, and smooth drying characteristics by treating the material with formaldehyde in aqueous phase in the presence of sulfur dioxide under controlled moisture conditions at a temperature between about 65 and C. or higher, e.g., in a chamber heated to between about 80 and C.

The process, which is applicable to flat fabrics as well as completed garments, requires relatively short reaction times, gives high wrinkle recoveries and at the same time produces satisfactory tensile and tear strengths without requiring an after-wash of the treated fabric.

According to the invention claimed herein the cotton or other cellulose-containing fabric such as a cottonpolyester blend is impregnated with a liquid solution containing about 2 to 40 per cent, preferably 10 to 30 per cent, formaldehyde in water or similar liquid solvent to give a wet pick-up of between about 50 and l 10 per cent based on dry cotton weight. The fabric is then conditioned or dried to a moisture content of between about 4 and 20 per cent, preferably between about 10 or 12 and 18 per cent, passed into or placed in an atmosphere containing sulfur dioxide gas in a concentration which may range from as little as (H volume per cent on up, for instance, 5 to 30 volume per cent sulfur dioxide, and maintained in the presence of sulfur dioxide under controlled moisture conditions at a temperature between about 80 and l50C. or higher, for a time of between about seconds and 2 hours, for instance, 30 seconds to 5 minutes, until the proper amount of formaldehyde is durably deposited or fixed in the fabric. Satisfactory durable wrinkle recovery and tear strength are obtained when formaldehyde is durably fixed in the fabric in an amount which may range from about 0.3 per cent on upward, e.g., between 0.3 and 5 per cent, based on the weight of the cellulose fibers in the fabric. When the vapor treatment is performed batchwise rather than by passing a stream of sulfur dioxide gas through the treating chamber, very small concentrations of SO gas, e.g., as little as 0.1 volume per cent, are sufficient to produce the required amount of catalyst because the reactive S0 gas tends to be absorbed in the moist fabric and thus builds up a suitable effective concentration therein.

The optimum reaction time under any given set of reaction conditions is one which is just long enough to effect the desired degree of crosslinking without unnecessarily overexposing the fabric to the acid catalyst. lncreasing the reaction temperature or, surprisingly, increasing the moisture content of the reactive atmosphere or of the fabric permits reducing the reaction time under otherwise comparable conditions, and vice versa.

The moisture content of the fabric to be treated is important in this invention. Water is the limiting factor in the reaction of sulfur dioxide and formaldehyde which forms the required strong acid catalyst and which determines the extent of crosslinking of the cellulose by reaction with formaldehyde. Removal or displacement of water from the reaction system causes the system to be self-limiting and readily controllable. The strong but unstable catalyst makes the process fast as well as easy to control in a reproducible fashion. lnitial moisture in the fabric serves to swell the cellulose fibers and to hold therein the formaldehyde, the sulfur dioxide and the resulting acid catalyst in an aqueous phase, but has only a relatively small effect on the total amount of formaldehyde which is incorporated into the fabric in both fixed and unfixed form. Nevertheless, because of its role in the formation of the acid curing catalyst and in swelling the cellulose fibers, such initial moisture and its subsequent evaporation have a significant effect on wrinkle recovery and flex abrasion characteristics of the cured fabric. Wet wrinkle recovery improvement is produced principally when the fibers are crosslinked while in a water swollen state whereas dry wrinkle recovery improvement is produced in the process principally after most of the initial moisture has evaporated from the fibers and they are crosslinked in a neardry, collapsed state.

Generally speaking, too little initial moisture gives low wrinkle recovery values while too much moisture can cause excessive degradation of the fabric because of hydrolysis of the cellulose by the strong acid catalyst formed in the process. The amount of acid catalyst formed in the presence of water also affects the proportion of formaldehyde which actually forms durable crosslinks in the fabric as against that which is merely present as formaldehyde polymer.

For optimum control, the moisture content of the treating atmosphere is desirably maintained between about 10 and volume per cent, whereby evaporation of moisture from the fabric is retarded and the cellulose crosslinking reaction proceeds at a high rate while the cellulose fibers are in a water swollen condition. When the initial moisture content of the fabric introduced into the curing chamber is low such that the fabric dries rapidly on heating and the amount of acid catalyst formed is insufficient for assuring that the fon'naldehyde crosslinking reaction proceeds to the desired extent, one can make up for this by injecting steam into the reaction chamber and thereby increase the humidity of the system to the desired level as needed, as originally disclosed in our parent application Ser. No. 706,792, now abandoned, and our copending Ser. No. 239,361, now abandoned.

Because of its chemical function in this process, water plays an unusual role here in that the crosslinking reaction automatically tends to come to a stop when water evaporates from the fabric to a point where insufficient acid catalyst is formed or present to promote the crosslinking reaction. Whereas previous formaldehyde crosslinking processes were difficult to control, the decomposition of the catalyst upon drying makes the present process self-limiting in a desirable manner and makes it possible to produce a dry, crosslinked fabric which is essentially neutral upon removal from the high temperature treatment because dissipation of moisture from the hot fabric automatically results in the removal of any residual catalyst therefrom. Moreover, such formaldehyde polymer as is left on the treated fabric at the end of the curing or crosslinking step can be easily and permanently removed therefrom by simple heating, for instance, by heating the cured fabric in a stream of air or a mixture of air and high temperature steam or other nonreactive gas at a temperature above C, preferably between l00 and C. Such heating and stripping causes drying and decomposition of the acid catalyst as well as depolymerization and removal of unreacted formaldehyde from the cured fabric. This precludes liberation of irritating formaldehyde from the fabric during subsequent use and is in contrast to the behavior of urea-formaldehyde or melamineformaldehyde crosslinking resins, which tend to decompose slowly and release formaldehyde odors gradually from treated fabrics during service.

The fabric can be conditioned to give the desired initial moisture content by any suitable method, such as by padding the fabric with aqueous formaldehyde and partially drying or by holding a dried fabric for a time at a suitable temperature and relative humidity until it reaches the desired moisture regain.

Instead of impregnating the fabric directly with an aqueous formaldehyde solution, it is possible to provide such a solution in the fabric by first steaming or otherwise humidifying it to give it an appropriate moisture content, e.g., ID to 15 per cent regain, and then releasing formaldehyde vapors in a chamber where the humidified fabric is held at or near ambient temperature, e.g., between 15 and 45C., preliminary to the eventual heating and curing step. As a result, the formalde hyde vapors condense and dissolve in the moisture held in the fabric during such a preliminary impregnation step, prior to the curing step. The impregnation with aqueous formaldehyde solution and the subsequent curing in the controlled presence of moisture and added sulfur dioxide can be carried out consecutively in the same chamber, or separately in consecutive chambers.

Furthermore, it is possible to release not only formaldehyde vapor but also sulfur dioxide gas in such a preliminary impregnation step and thus dissolve both the required formaldehyde and the required sulfur dioxide in the conditioned or humidified fabric which is at ambient or relatively low temperature. In such a case no sulfur dioxide need to be added in the subsequent high temperature curing step.

Other, optional features of the invention include the addition of various monomeric or polymeric additives which serve to alter fabric properties. For instance, treatment of the cloth prior to the S treatment with a compound having an active hydrogen, and particularly with a hydroxyl compound such as ethylene glycol, triethylene or tetraethylene glycol dimethyl ether, glycerine, glycidol and the like, surprisingly results in a substantially greater increase in wet wrinkle recovery than dry wrinkle recovery, and can be used for this purpose when such an effect is desired. Other useful additives having an active hydrogen compound include amides such as urea proper or other ureas, e.g., cyclic ethyleneurea, allylurea and thiourea, acetamide, malonamide and acrylamide as well as sulfonamides such as methanesulfonamide; carbamates such as ethylcarbamate or hydroxyethylcarbamate; and so on. When such monomers which contain an active hydrogen are treated with formaldehyde in accordance with the present invention, they become fixed on the fabric so that they do not wash out. At dry add-ons of about 5 per cent, e.g., between 5 per cent and per cent pretreatment with the amides, and especially with urea, they tend to lead to unusually high tensile and tear strength retentions. They also add crispness to the fab ric after being fixed thereon by the formaldehyde.

Moreover, pretreatment of the cloth, prior to the S0 treatment, with polymeric resinous additives that form soft films, such as conventional dispersions or latexes, can result in an unusually great incremental improvement in wrinkle recovery as compared with similar effects when such additives are used in conjunction with more conventional crosslinking treatments. Polymers can also improve the flex abrasion resistance and tear strength, or alter the ratio of dry wrinkle recovery to wet wrinkle recovery, or in some instances shorten the reaction time needed to produce an acceptable durable press fabric. Polymeric additives suitable for such purposes are, in most cases, available commercially in concentrated aqueous latex form, and it is desirable to dilute these to a concentration of l to 3 per cent polymer before padding onto the fabric. Suitable polymeric additives include solid resinous or rubbery acrylonitrilebutadicne copolymers and mixtures containing the same with various vinyl resins; polyethylene; deacetylated copolymers of ethylene and vinyl acetate; polyurethanes; and various polymers of alkyl acrylates, other polyesters and polyamides. Coating of the fabrics with such polymers subsequent to the formaldehyde treatment may also be used to give similar results.

The present invention is useful for treating various natural or artificial cellulosic fibers alone or as mixtures with each other in various proportions or as mixtures with other fibers. Such natural cellulosic fibers include cotton, linen and hemp, and regenerated or artificial cellulosic fibers useful herein include, for example, viscose rayon and cuprammonium rayon. Other fibers which may be used in blends with one or more of the above mentioned cellulosic fibers are, for example, cellulose acetate, polyamides, polyesters, polyacrylonitrile, polyolefins, polyvinyl chloride, polyvinylidene chloride and polyvinyl alcohol fibers. Such blends preferably include at least 15 or 20 per cent by weight and most preferably at least 35 or 40 per cent by weight, of cotton or natural cellulose fibers. Blends containing 50 to per cent cotton and correspondingly 50 to 20 per cent polyester fiber are eminently suited for treatment according to this invention.

The fabric may be knit, woven or non-woven, or be any otherwise constructed fabric. The fabric may be flat, creased, pleated, hemmed, or sewn or otherwise formed to produce an article such as a garment of any desired shape prior to curing. After processing, the formed crosslinked fabric will maintain substantially the original configuration for the life of the article, that is, a wash-wear or durable press fabric will be produced.

When treating with gaseous sulfur dioxide the conditioned fabric is passed into a treating atmosphere containing sulfur dioxide which may be obtained from any convenient source. In addition to the sulfur dioxide and water vapor, the treating atmosphere may contain inert gases such as air, nitrogen, carbon dioxide, helium, and the like. Since sulfur dioxide forms the required strong acid catalyst by reacting with formaldehyde and water in the fabric, sulfur dioxide as such need not be supplied to or present in the process over the entire duration of the crosslinking reaction, but its supply may be discontinued after the first minute or two or when an adequate supply of sulfur dioxide has been absorbed by the fabric. To take advantage of the self-limiting feature of this process, it can be advantageous to pass the fabric being treated through zones of progressively lower humidity. Obviously, a comparable self-limiting effect is not obtainable when the more common catalysts such as HCI, ammonium chloride or zinc nitrate are used.

To contact the fabric with the gaseous sulfur dioxide any suitable means may be employed. For example, a batch system utilizing a closed chamber or tube containing the gaseous sulfur dioxide may be used in which the conditioned, moisture-containing fabric may be placed and there exposed to the treating atmosphere for the appropriate time. As indicated earlier herein, the vapor treatment may be carried out either in the same chamber in which the impregnated fabric is actually cured or the vapor treatment and the hot curing step may be carried out consecutively in separate chambers. In the alternative, a dynamic or continuous system can be used containing a series of more or less distinct zones for conducting the desired combination of impregnation and conditioning, curing and purging steps through which the appropriate gases and the fabric or garments being treated are passed at appropriate rates relative to each other.

DESCRIPTION OF SPECIFIC EMBODIMENTS The present invention is further illustrated by the following examples.

Example 1 This is an illustrative example of sulfur dioxide catalyzed. formaldehyde solution treatment of cotton print cloth in accordance with the present invention.

A glass tubular reactor approximately 8 cm. in diameter and 40 cm. in length, wrapped with heating tape and mounted horizontally, was heated to the desired temperature. Sulfur dioxide was metered into the reactor from a storage tank to give a sulfur dioxide concen tration in the reactor atmosphere of 10 volume per cent, the remainder being ambient air.

and results for three runs where temperature as well as 25 duration of treatment were varied. As can be seen, operating at higher temperatures significantly improves the crease recoveries of the fabric while permitting shorter reaction times, which is commercially desirable.

Example 2 Table ll shows the data for a series of samples of print-cloth treated in accordance with this invention.

5 First the samples were padded with various aqueous solutions containing from 5 to 20 per cent formaldehyde, which in each case also included 3 per cent softener in the form of finely dispersed acrylic polymer (Rhoplex K-87 Latex). In addition, in the case of Sample lll6 10 the pad bath included 66 per cent aqueous isopropanol instead of water as the aqueous solvent; in the case of Sample ll-l7, the pad bath further included 5 per cent tripropylene glycol rnonomethyl ether as a humectant; and in the case of Sample [1-18, 5 per cent Span 20" sorbitan monolaurate. Excess solution was expressed from the samples on a pad roll to leave about 65 per cent wet pick-up based on the weight of the fabric and the samples were then cured by being exposed for various times to a stream of hot vapors of SO at widely different conditions in a l00 liter cylindrical aluminum reactor such as the one described in US. Pat. No. 3,706,526 at column 7, lines -38.

In the case of Samples "-5, "-6 and 11-7, the padded fabrics were dried in an air oven at C. for 3 minutes, 4 minutes and 3 minutes, respectively, before exposure to the hot SO vapors in the reaction chambers; all the other samples were placed in the reaction chamber without pre-drying. Of course, the samples progressively dry out in the reaction chamber in any event as 30 the hot treating gas is passed over them.

TABLE I Run l Run 2 Run 3 Formaldehyde in pad bath l3% l3% l3% Polyethylene in pad bath 2% emulsion 2% emulsion 2% emulsion Polyacrylate in pad bath 2% emulsion 2% emulsion 2% emulsion Fabric moisture content I09? I09? 10% Sulfur dioxide concentration [0% I0)? 10% Temperature 48C. C. 80C, Duration of treatment 20 min, 20 min. 10 min. Wash-wear rating [AATCC 88A l964T) 3.5 4.0 3.5 Wrinkle Recovery [AATCC 66-l959T) Dry 273 306 312 (W F) Wet 297 297 304 Elmendorf Tearing Strength [ASTM 04424-59) 725 grams 630 grams (140 grams Stoll Flex Abrasion Resistance [ASTM D-l l75-6lT) {using head and tension loads of A and 2 pounds, respectively) 490 280 430 TABLE [I PRINTCLOTH FABRICS TREATED WITH AQUEOUS FORMALDEHYDE AND CROSSLINKS BY HEATING IN PRESENCE OF SULFUR DIOXIDE Wrinkle Recovery Angle SO, Air Reaction (W-t-F) Tearing" Sample Pad Bath Flow Rate" Flow Rate Temp. Time Dry Wet Strength No. (%CH,0) (cc/min) (cc/min) (C.) (min) (degrees) (degrees) (grams) "-1 5 4 400 80 7 303 294 440 "-2 S 4 400 80 5 248 257 660 "-3 l0 8 400 80 5 300 296 470 "-4 l0 8 400 80 10 295 292 400 "-5 l0 8 400 80 5 293 286 400 11-6 10 8 400 80 5 266 269 540 "-7 l0 8 400 80 4 303 284 400 ll-8 I0 24 200 l00 S 323 289 350 "-9 I0 24 200 I00 4 263 254 790 ll-l0 It) 200 0 S 332 320 220 ll-ll 10 200 0 l05 4 328 CH3 240 ll-l2 20 200 0 I20 3 346 338 280 PRINTCLOTH FABRlCS TREATED WITH AQUEOUS FORMALDEHYDE AND CROSSLlNKS I3Y HEATING IN PRESENCE OF SULFUR DIOXIDE Wrinkle Recovery Angle (W+F) S Air Reaction Tearing" Sample Pad Bath Flow Rate" Flow Rate Temp Time Dry Wet Strength No. (%CH O) (cc/min) (cc/min) (C.) (min) (degrees) (degrees) (grams) "-1 3 20 200 0 I20 2 329 317 380 "-14 4 200 I 2 314 297 410 ll-IS 5 4 200 I20 3 315 295 400 "-16 I0 4 400 l20 5 302 309 420 "-17 l 4 400 I 5 316 283 420 "-1 8 l 4 400 I40 5 304 286 300 Untreated Control n.a. n.a. n.a. n.a. n.a I66 129 750 Properties After 10 Laundering Cycles Wrinkle Recovery Angle (W+F) Tearing Sample Dry Wet Strength No. (degrees) (degrees) (grams) ll-l0 lI-l l ll-l2 ll l 3 334 3! l 300 ll 14 320 284 450 [H5 315 2B] 460 "-16 306 280 400 "-17 304 2B] 340 n.a. not applicable. a. i The exacl concentration of SO, in the reactor was not determined. h After I laundering cycle.

Upon conclusion of the treatment the essentially dry Example 3 and neutral samples were removed from the reactor and washed and tumble dried so that their durable press ratings could be determined. These ratings were determined after one such laundering-drying cycle and after 10 such cycles.

As can be seen from Table ll. high dcgrccs ofdry and wet rccovcry could be obtained under a wide variety of treating conditions, with formaldehyde concentrations in the pad bath ranging from as little as l per cent up to 20 per cent.

At high SO concentrations and at a temperature of 120C. (Samples Ill0, "-11, [1-12 and ll-l3), the crosslinking reaction proceeds very rapidly such that very high degress of wrinkle recovery are achieved in 2 minutes or less. whereas at longer reaction times the fabric becomes progressively weaker due to exposure to the large amount of strong acid formed in the process.

lfthe fabric is dried to a relatively low initial moisture content prior to heating in the presence of catalystforming S0 lower wrinkle recoveries are obtained in this system than when the reaction is initiated at a relatively higher moisture content under otherwise similar conditions. (Compare Samples 0-6 with Samples "-5 and 0-7.)

At relatively high initial moisture contents and relatively low reaction temperatures, higher wrinkle recoverics may be obtained by increasing the reaction time or the S0 concentration in the treating atmosphere. Compare Sample "-2 with Samples "-1 andll-3, and Sample "-9 with Samples "-8 and "-1 l.

In this series of tests, samples of twist twill cotton fabric of 7.8 oz./sq. yd. weight were padded with an aqueous solution containing 7.5 per cent formaldehyde and l0 per cent "Rhoplex K-ST finely dispersed acrylic polymer, cxcess solution was expressed from the samples on a pad roll to leave about 65 per cent wet pickup based on the weight of the fabric, the samples were then exposed for l to 5 minutes (as shown in Table III) to a stream of S0 gas at a temperature of 20C. in the reactor described in Example 2 and then (except in the case of Samples Ill-8 and Ill-9, which were not further treated) the fabrics containing formaldehyde and S0 absorbed therein were cured for 5 minutes in an oven which had been preheated to 150C.

In the case of Samples [ll-l, "1-2 and [ll-3, the padded fabrics were partially dried in air at room temperature to an estimated moisture content of about l0 per cent on weight of fabric before being placed in the reactor and exposed to the gas. Samples Ill-4, Ill-5, Ill-6, "1-8 and lll9 were partially dried for 5 minutes in an air oven at 80C. to reduce their moisture before exposure to the S0 gas; and Sample [ll-7 was exposed to the S0 wet, without any significant drying between padding and exposure to the SO, gas. Samples [ll-l through [ll-7 were washed and tumble dried after their high temperature cure while Samples Ill-8 and Ill-9 were washed and tumble dried directly after the S0 treatment before the durable press properties of these samples were determined. The results are shown in Table lll.

TABLE m TWlLL COTTON FABRICS TREATED WITH AQUEOUS FORMALDEHYDE AND SULFUR DIOXIDE AND THEN HEATED Wrinkle Recovery Angle Stoll Flex 1 degrees 1 Abrasion Sample SO, Exposure Postheating Time Dry Wet Warp No. Time (min) at 150C. (min) Warp Fill Warp Fill (cycles) 111-1 1 S 156 144 151 136 248 111-2 3 161 152 155 148 132 111-3 5 5 167 148 164 151 ill-4 l 5 123 134 843 111-5 3 5 154 132 149 132 704 Ill-6 5 5 162 154 134 221 111-7 1 S 167 170 162 48 H3 1 0 84 90 82 84 1202 l1l-9 5 0 92 82 88 86 1748 Untreated Control 80 74 76 72 505 Tensile Properties Warp Fill Work-to Extension Breaking Work-to Extension Breaking Sample Rupture at Break Strength Rupture at Break Strength 0. (in-1b) (lb) tin'lb) (91 (lb) l11-1 9.1 9.0 87.1 1.9 13.2 21.1! 111-2 61 8.0 70.7 1.6 9.9 16.0 111-3 60 8.2 60.6 1.6 10.2 16.5 1114 18.4 13.6 120.0 2.5 12.0 246 ill 5 12.1 10.6 99.2 3.0 12.2 27.6 Ill-6 7.9 8.9 79.5 2.6 12.3 24.6 ill-7 2.5 6.4 48.0 1.1 9.2 10.6 Ill-8 36.6 22.1 163.1 12.1 19.1 66.1 [1L9 34.11 21.8 158.3 11.9 20.0 67.2 Untreated Control 305 13.4 171.0 11.2 17.2 66.7

Samples Ill-l through Ill-7, which had the S0 gas applied thereto at room temperature and were then oven cured, all exhibited a high degree of wrinkle recovery. (In comparing Tables [I and [[1, it should be noted that in Table I] the reported wrinkle recovery angles are the sum of the values measured in the warp and in the fill directions, whereas in Table lll each of these two values is reported separately.)

Sample lll-7, which was not conditioned prior to exposure to the S0 gas, evidently underwent the highest degree of crosslinking, as indicated by the high wrinkle recovery angles. However, its tensile properties also were the lowest among those reported, because of fabric degradation due to the relatively large amount of strong acid present in the hot cure in this case.

At the other extreme, Samples Ill-8 and ill-9 which were not heat cured after treatment with the 80;. gas at room temperature showed only an insignificant improvement in durable press properties and only comparatively minor changes in tensile properties as compared with the untreated control, although the increase in tearing strength obtained as a result of the cool S0 treatment is worth noting.

In the absence of a final high temperature cure, little difference is observed between the oven dried Sample ill-8 which was exposed to S0 gas for 1 minutes and the similarly dried Sample [ll-9 which was exposed to SO gas for 5 minutes. On the other hand, a comparison between Samples 111-4, 111-5 and Ill-6 shows that the extent of formaldehyde crosslinking of the fibers increases with an increase in time of the S0 pretreatment. This is reflected both in the increasingly high recovery angles and in the decreasing tearing strengths. Evidently. more acid catalyst is present in the high temperature cure as the duration of the S0 pretreatment of the moist fabric is increased. A similar effect is ohserved when Samples Ill-1, ill-2 and lll3 are compared with each other.

An increased intensity of treatment is also observed when one compares Sample lll-l against Hi4, Ill-2 against 111-5, and Ill-3 against Ill-6. Evidently, more moisture and therefore more acid catalyst is present in the samples which were conditioned in air at room temperature prior to the S0 treatment than in those which were conditioned by being partially dried at 80C. for a short time.

No attempt was made in this series of tests to optimize either the initial moisture conditioning or the final curing conditions. However, the tests demonstrate that S0 can be absorbed in the formaldehyde-containing aqueous phase in the fabric at relatively low temperature prior to curing the fabric at an elevated temperature.

Example 4 Still another procedure was used in this series of tests in depositing an aqueous phase containing formaldehyde and SO, in samples of the twist twill fabric described in Example 3 prior to a final curing step. In this series the fabrics were padded with a bath containing 3 per cent acrylic polymer solids (Rhoplex [(-87 Latex), partially dried in an air oven for 5 minutes at 80C., exposed to formaldehyde-sulfur dioxide vapors at 120C. for 1 minute in the reactor described in Example 2 above, removed from the reactor and then immediately post-cured by being placed for 5 minutes in an air oven which had been preheated to a specific temperature between 120 and C, as indicated in Table IV. The cured samples were finally washed and tumble dried as usual before determining their durable press and tensile properties. For control purposes, in

Stoll Flex Abrasion Warp (cycles) 14 cured. In the latter case, the l minute treatment with formaldehyde and S vapors at l20C. in the absence of any added steam was insufficient to permit crosslinking of the cellulose with formaldehyde to proceed to the desired extent. On the other hand, in all the other cases the heat soaking step immediately following the formaldehyde-SO vapor treatment of the moist fabric produced a good balance of durable press and tensile properties. This shows that exposure of a moist fabric to 3 TABLE W Properties After 1 Washing Wrinkle Recovery Angle (degrees) Warp Fili Wash-Wear Dry Wet Dry Wet Rating properties, the gent and tumble -wear ratthe convery high crease ree of all samples with 11 which was not post- ONE MINUTE AND THEN HEAT SOAKED AT ll60"C.

Heat-Soaking Temp. ("0) 13 the case of Sample lV-l l the final posbcuring step was omitted.

To test their durable press and tensile treated samples were washed in deter dried and their wrinkle recovery angles, wash ings and tensile properties were measured in ventional manner.

As can be seen from Table IV, coveries were obtained in the cas the exception of Sample IV- CONDITIONED TWIST TWILL FABRICS EXPOSED T0 FORMALDEHYDE SULFUR DIOXIDE FOR Sample No.

0 0 00 00 00000000000 2444333256 33233 22462 8 l l m 5 2 u .N m A w!) nb 328040828 302020 4940 4 m 33333323330 43333333336 6 ssznoziszos zssoyojnns a T9 4444444442W33343434432 n o r P M H mw 4 .4.4.7.0 .4.2- 4456342321 66205346807 42036206885 5 F m m w .QUMMMDNHUUM UUHHUUUUUHM W n. M n i I 2088028 234 07 0408686 6 h om m unnnnnwmnum uunnuunnmu s a m mwn 131 31125 sJJsJe EsA a ,1 IP 33433223439w 42323223338 0 n n n m w x 59005 764404 0053000887 e r. r 4444%465440 4344453339 7 .n P m A .P. h A s :l e .m m mum a n e e 3724424462 26622828997 2 muwwmwmfimnw mmmuwmmmmn% w. T E mUw sssa999799M w I l l l l l l l l l l l l l l l l l II M w P m as) annsszsossz 135322 133 a mo 4435344446 45555764656 1 1 W l l l l l l l l l I1 llllllll I1 2 d M m E3 00000000 u 0000000000 u wm55443322C 6655443322C A I l l l i I l 3 ll. llllllllllllll n We) 0 0 [Y N N bm Js52 .s 0 3 .19 .45 0 l P 00200 0274 0 00 4 8430 4 MM l l l l l l l .ll l l l l l ll. I1 3 d d mm c mm O e" M. H 0 daaadsJss i J$ .mm m 444464 8844 444466 44044Mm a wwwwwwwwwww wwwwwwwwwwwuc sN lwwwwwwwwww wwwwwwwwwwwuc formaldehyde and S vapors under mild conditions which are insufficient to impart the desired durable press properties to the fabric can in fact form a catalyzed reactive aqueous formaldehyde phase in the fabric such that the latter, having a proper initial moisture content, can be subsequently crosslinked to the desired extent by further heat treatment without adding any more SO or formaldehyde to the system.

It should be understood, of course, that even in the case of a vapor treatment such as that used in preparing Sample lVl l satisfactory durable press properties can be obtained directly by a proper control of treating conditions as disclosed in our US. Pat. No. 3,706,526, without any separate post-cure, e.g., by applying the vapor treatment to the initially moist fabric at a higher temperature or for a longer time or under more moist conditions, as by reducing the rate of vapor flow through the reactor or by adding stream to such vapors, or by a combination of these factors.

A procedure of this type, involving chemical pretreatment under relatively mild conditions followed by a separate heat soaking step of the pretreated, preconditioned fabric in hot air or a hot air-steam mixture under controlled moisture conditions may be particularly advantageous in the continuous processing of flat fabrics.

The effects of moisture content, of amount of formaldehyde durably fixed in the fabric and of additive pretreatments are similar in this system wherein formaldehyde is applied in liquid phase, as in the vapor phase system described in parent application Ser. No. 706,792 filed Feb. 20, 1968 and now abandoned, and in US. Pat. No. 3,706,526 which was filed as a continuation-in-part of the former.

While all of the above runs were conducted at atmospheric pressure, subor superatmospheric pressures may be used but are not necessary.

The essential principles, as well as the preferred embodiments and modes of operating of the present invention have been described in the foregoing specification. However, the invention which is intended to be protected herein may be practiced otherwise than as described without departing from the scope of the appended claims.

What is claimed is:

l. A process for improving the dimensional stability, wrinkle resistance and smooth drying characteristics of a cellulose fiber-containing fabric which comprises:

a. depositing water and formaldehyde in the fabric to provide therein an aqueous phase comprising formaldehyde and conditioning the fabric to give the cellulose fibers a moisture content of between about 4 and 20 percent based on dry weight of cellulose;

b. heating the conditioned moisture-containing and formaldehyde-containing fabric in the presence of catalyst-forming sulfur dioxide and water vapor in a reaction zone at a temperature above about 65C. for a time of between about seconds and 2 hours until formaldehyde in an amount equal to at least 0.3 percent by weight of said cellulose fibers is durably deposited in the fabric and the cellulose fibers become effectively crosslinked, said heating being conducted while governing the amount of water in the system to control the amount of moisture in said fabric and thereby regulate the amount of strong acid catalyst formed therein by the reaction of formaldehyde and sulfur dioxide, a reaction in which water is the limiting factor, to provide a self-limiting reaction system; and

c. heating the thus crosslinked fabric to dissipate water vapor, residual catalyst and unbound formaldehyde therefrom.

2. A process according to claim 1 wherein the fabric is heated in step (b) to a temperature between about 80 and about l50C. and is dried and unbound formaldehyde is vaporized therefrom by heating it in step (c), thereby directly producing a dry, crosslinked, essentially neutral fabric.

3. A process according to claim 1 wherein the fabric is treated prior to the formaldehyde crosslinking step with a compound containing an active hydrogen and selected from the group consisting of polyhydric alcohols, ureas, amides and carbamates.

4. A process according to claim 1 wherein the conditioned moisture-containing fabric is treated with sulfur dioxide gas before being heated in said reaction zone in step (b).

5. A process according to claim 1 wherein the fabric is one containing at least 35 percent by weight of cotton and wherein the aqueous formaldehyde solution contains between about 1 and 40 percent by weight of formaldehyde.

6. A process for improving the dimensional stability, wrinkle resistance and smooth drying characteristics of cottoncontaining fabrics which comprises:

a. applying to the fabric an aqueous solution containing about 2 to 40 percent by weight of formaldehyde and conditioning the fabric to give the cotton a moisture content of between about 4 to 20 percent based on dry weight of cotton;

b. heating the conditioned moisture-containing and formaldehyde-containing fabric to a temperature of between about 80 and about l50C. in the presence of sulfur dioxide in an atmosphere containing water vapor in a reaction zone for a time of be tween about 10 seconds and 2 hours until formaldehyde in an amount equal to at least 0.3 percent by weight of said cotton is durably fixed in the fabric and the cotton fibers are effectively crosslinked, said heating being conducted while governing the amount of water in the reaction zone to control the amount of moisture in said fabric and thereby regulate the amount of strong acid catalyst formed therein by the reaction of formaldehyde and sulfur dioxide, a reaction in which water is the limiting factor, to provide a self-limiting reaction system; and

c. at the end of said crosslinking step (b) removing residual catalyst and unbound formaldehyde from the fabric by heating it in an inert gaseous atmosphere, thereby directly producing a dry, crosslinked, essential neutral fabric.

7. A process according to claim 6 wherein steam is injected into the reaction zone in step (b) to adjust the water vapor concentration therein at between about 10 and per cent by volume and thereby to retard evaporation of moisture from the conditioned fabric and control the crosslinking reaction.

8. A process for improving the dimensional stability, wrinkle resistance and smooth drying characteristics of cotton-containing fabrics which comprises:

impregnating in the fabric an aqueous solution con- ,taining about 10 to 30 percent formaldehyde;

drying and conditioning the impregnated fabric to a moisture content of between about 4 to 20 percent;

heating the moisture-containing and formaldehydecontaining fabric in a reactive gaseous atmosphere comprising water vapor and about 0.1 to 30 volume per cent sulfur dioxide at a temperature between about 90 and about 150C. for a time of hyde and sulfur dioxide, a reaction in which water is the limiting factor, to provide a self-limiting reaction system; and

drying the thus crosslinked fabric.

9. A process according to claim 8 wherein the fabric is treated in a pad bath containing an amide prior to moisture conditioning.

10. A process according to claim 8 wherein urea or thiourea is applied to the fabric together with the formaldehyde solution.

11. A process according to claim 10 in which the fabric being treated is a flat fabric and the crosslinkcd fabric is washed to remove residual reactants therefrom,

and the washed, crosslinked fabric is dried. 

1. A PROCESS FOR IMPROVING THE DIMENSIONAL STABILITY WRIN KLE RESISTANCE AND SMOOTH DRYING CHARACTERISTICS OF A CELLULOSE FIBER-CONTAINING FABRIC WHICH COMPRISES: A. DEPOSITING WATER AND FORMALDEHYDE IN THE FABRIC TO PROVIDE THEREIN AN AQUEOUS PHASE COMPRISING FORMALDEHYDE AND CONDITIONING THE FABRIC TO GIVE THE CELLULOSE FIBERS A MOISTURE CONTENT OF BETWEEN ABOUT 4 AND 20 PERCENT BASED ON DRY WEIGHT OF CELLULOSE; B. HEAING THE CONDITIONED MOISTURE-CONTAINING AND FORMALDEHYDE-CONTANING FABRIC IN THE PRESENCE OF CATALYST-FORMING SULFUR DIOXIDE AND WATER VAPOR IN A REACTION ZONE AT A TEMPERATURE ABOVE ABOUT 65*C FOR A TIME OF BETWEEN ABOUT 10 SECONDS AND 2 HOURS UNTIL FORMALDEHYDE IN AN AMOUNT EQUAL TO AT LEAST 0.3 PERCENT BY WEIGHT OF SAID CELLULOSE FIBERS IS DURABLY DEPOSITED IN THE FABRIC AND THE CELLULOSE FIBERS BECOME EFFECTIVELY CROSSLINKED SAID HEATING BEING CONDUCTED WHILE GOVERNING THE AMOUNT OF WATER IN THE SYSTEM TO CONTROL THE AMOUNT OF MOISTURE IN SAID FABRIC AND THEREBY REGULATED THE AMOUNT OF STRONG ACID CATALYST FORMED THEREIN BY THE REACTION OF FORMALDEHYDE AND SULFUR DIOXIDE, A REACTION IN WHICH WATER IS THE LIMITING FACTOR, TO PROVIDE A SELF-LIMITING REACTION SYSTEM AND C. HEATING THE THUS CROSSLINKED FABRIC TO DISSIPATE WATER VAPOR, RESIDUAL CATALYST AND UNBOUND FORMALDEHYDE THEREFROM.
 2. A process according to claim 1 wherein the fabric is heated in step (b) to a temperature between about 80* and about 150*C. and is dried and unbound formaldehyde is vaporized therefrom by heating it in step (c), thereby directly producing a dry, crosslinked, essentially neutral fabric.
 3. A process according to claim 1 wherein the fabric is treated prior to the formaldehyde crosslinking step with a compound containing an active hydrogen and selected from the group consisting of polyhydric alcohols, ureas, amides and carbamates.
 4. A process according to claim 1 wherein the conditioned moisture-containing fabric is treated with sulfur dioxide gas before being heated in said reaction zone in step (b).
 5. A process according to claim 1 wherein the fabric is one containing at least 35 percent by weight of cotton and wherein the aqueous formaldehyde solution contains between about 1 and 40 percent by weight of formaldehyde.
 6. A process for improving the dimensional stability, wrinkle resistance and smooth drying characteristics of cottoncontaining fabrics which comprises: a. applying to the fabric an aqueous solution containing about 2 to 40 percent by weight of formaldehyde and conditioning the fabric to give the cotton a moisture content of between about 4 to 20 percent based on dry weight of cotton; b. heating the conditioned moisture-containing and formaldehyde-containing fabric to a temperature of between about 80* and about 150*C. in the presence of sulfur dioxide in an atmosphere containing water vapor in a reaction zone for a time of between about 10 seconds and 2 hours until formaLdehyde in an amount equal to at least 0.3 percent by weight of said cotton is durably fixed in the fabric and the cotton fibers are effectively crosslinked, said heating being conducted while governing the amount of water in the reaction zone to control the amount of moisture in said fabric and thereby regulate the amount of strong acid catalyst formed therein by the reaction of formaldehyde and sulfur dioxide, a reaction in which water is the limiting factor, to provide a self-limiting reaction system; and c. at the end of said crosslinking step (b) removing residual catalyst and unbound formaldehyde from the fabric by heating it in an inert gaseous atmosphere, thereby directly producing a dry, crosslinked, essential neutral fabric.
 7. A process according to claim 6 wherein steam is injected into the reaction zone in step (b) to adjust the water vapor concentration therein at between about 10 and 70 per cent by volume and thereby to retard evaporation of moisture from the conditioned fabric and control the crosslinking reaction.
 8. A process for improving the dimensional stability, wrinkle resistance and smooth drying characteristics of cotton-containing fabrics which comprises: impregnating in the fabric an aqueous solution containing about 10 to 30 percent formaldehyde; drying and conditioning the impregnated fabric to a moisture content of between about 4 to 20 percent; heating the moisture-containing and formaldehyde-containing fabric in a reactive gaseous atmosphere comprising water vapor and about 0.1 to 30 volume per cent sulfur dioxide at a temperature between about 90* and about 150*C. for a time of from about 10 seconds to about 2 hours until formaldehyde in an amount equal to at least 0.3 percent by weight of said cotton fibers is durably fixed in the fabric and the cotton fibers are effectively crosslinked, said heating being conducted while governing the amount of water vapor in said atmosphere to control the amount of moisture in said fabric and thereby regulate the amount of strong acid catalyst formed by the reaction of formaldehyde and sulfur dioxide, a reaction in which water is the limiting factor, to provide a self-limiting reaction system; and drying the thus crosslinked fabric.
 9. A process according to claim 8 wherein the fabric is treated in a pad bath containing an amide prior to moisture conditioning.
 10. A process according to claim 8 wherein urea or thiourea is applied to the fabric together with the formaldehyde solution.
 11. A process according to claim 10 in which the fabric being treated is a flat fabric and the crosslinked fabric is washed to remove residual reactants therefrom, and the washed, crosslinked fabric is dried. 